I think you've found a great place to come to learn and understand about the unfortunate situation you are faced with. Those of us who have traveled this road will advise you to stand firm with the boundary you set.
The line you drew in the sand is an important one, it's an empowering one and a freeing one for YOU. All too often we codies keep moving that line back and as sure as you and I are breathing right now, the addicts will cross it, again and again.
But this is your journey your time to learn and understand the realities of this disease and about yourself and your reactions to it.
No matter what next step you take, what decisions you make, know there is comfort and understanding among us.